A new type of agriculture has recently taken shape in American cities. Vacant properties and high-rise rooftops are morphing into farms, yielding fresh produce and honey, and exposing urban dwellers to the once strictly rural activity of food production. But sadly (and perhaps nor surprisingly), it might be a passing fad.

At least that’s what a new study published in the British Food Journal suggests. Carolyn Dimitri, the lead author and an associate professor of food studies at New York University, set out to assess the viability of American urban farming and to identify what drives urban farmers. She and her colleagues found that about two-thirds had a social mission that went beyond food production and profit. She also found that, regardless of their mission, roughly two-thirds of urban farmers say they’re failing to make a living, reporting sales below $10,000 per year.

In a survey of 370 farmers working in or around U.S. cities, Dimitri and her colleagues posed questions addressing what and how much they produce, how they sell and market their products, the risks and challenges of urban farming, and the farm’s size and characteristics. The researchers allowed the survey respondents to self-identify, so the respondents came from a range of farm types—vertical farms, hydroponic farms, crops planted on large parcels, on tiny lot corners and on rooftops, non-profit and for-profit, located within the downtown of a city, in the suburbs, or even in peri-urban areas.

Most farms reported sales below $10,000 per year.

The majority of urban farmers said that they were producing food not only for profit, but also to educate community members, improve food security, and build community. But only one-third said that they operated as non-profits. Roughly the same number reported earning a living off their farm. (There was no correlation between profit status and profit margin, however.) This raises questions about the long-term financial viability of most of these farms, located as they are on relatively expensive land with little revenue to support them.

These findings are not necessarily representative of the whole country. Since there is no authoritative list of every urban farm in America, Dimitri collected the survey sample by sending out requests on farming listservs and social media. So there may be some selection bias at work.

Still, the overwhelming rate of urban farmers expressing social motives, and extremely low profits, can’t be ignored. Dimitri notes that the non-profit model might be a good one for all of these socially conscious farmers, since they can find grants and donations to cover their shortfalls while they’re scaling up food-production profits.

But in the long-term, with precious few urban farmers making a livings, “I wonder if 10 years down the line, people will be tired of working really hard without making a good living,” she tells CityLab. “I wonder if urban farming might just be a passing trend that fades into the background.”